Temperatures are plummeting into the low 30s at night, but Eastern equine encephalitis and West Nile virus continue to pose a threat.
A batch of mosquitoes from Stratham that tested positive for West Nile yesterday is a strong indication the public must still protect themselves from mosquitoes, said Beth Daly, chief of infectious disease surveillance with the state Department of Health and Human Services.
“We still think there is a risk out there,” Daly said. “People should continue to take precautions.”
Those precautions include wearing long-sleeved clothing and using insect repellent.
The recent chilly weather can be misleading, she said.
“There are still mosquitoes out there,” Daly said. “I think the populations have been going down with the cold weather, but they are still out.”
Two hard freezes are needed to kill off mosquitoes carrying the potentially deadly viruses, according to Sarah MacGregor, owner of Dragon Mosquito Control.
The temperature dropped to about 30 degrees early Saturday, slightly below freezing.
“I was hoping it was 25 degrees,” MacGregor said. “It wasn’t cold enough for long enough.”
The National Weather Service defines a hard freeze as temperatures dropping below 28 degrees at any time or at least below 32 degrees for three hours or longer.
Although Southern Hampshire was spared frost, most of southern New England experienced a hard freeze that day, according to the National Weather Service.
The mercury was expected to drop to 33 degrees overnight, with nighttime temperatures hovering in the 40s the rest of the week. Daytime temperatures are to be in the 50s and 60s.
Daly said the state wrapped up its testing yesterday, and MacGregor said Dragon has stopped trapping mosquitoes.
The 41 mosquito batches that tested positive for West Nile are the most ever in New Hampshire, Daly said. The next highest number was 33 in 2002, she said.
The batch from Stratham was trapped Oct. 10 — the same day a horse in Durham was diagnosed with EEE. A horse in Derry contracted EEE three weeks ago and died.
It’s extremely rare for an animal with EEE to survive, MacGregor said.
Nine mosquito batches tested positive for EEE in the state this year, including Sandown, Newton and Danville, where infected mosquitoes were trapped on the grounds of Danville Elementary School on Sept. 27.
School Superintendent Earl Metzler ordered that students be kept inside during recess. The order was lifted Oct. 9 because of the reduced threat.
MacGregor said only a couple of mosquitoes a day were being caught in traps when the trapping ended late last week.
The nine EEE cases may seem like a lot, but not compared to the 73 batches of mosquitoes that tested positive in 2009, MacGregor said.
Then there was 2005, when seven humans contracted EEE, including two Newton residents. One, 20-year-old Kelly Labell, later died.
A Manchester man was the only person in New Hampshire to contract West Nile this year. No human cases of EEE were reported in the state.
In Massachusetts, an Amesbury woman with EEE died Sept. 24 and a Georgetown man with the virus died Sept. 27.
Although the first cases of infected mosquitoes are usually in August, the threat began early, MacGregor said.
“It was July when it started,” she said. “It certainly wears on people.”
MacGregor said she will be relieved when the threat ends. On many days, her staff has been working from 7 a.m. to nearly midnight.
“These people are definitely ready for a vacation,” she said.
But even after two hard freezes, people should be careful of mosquitoes hiding in enclosed spaces, such as barns or homes, MacGregor said.
Years ago, a horse contracted EEE just before Thanksgiving, she said.
“You would hope you’re done thinking about that and focusing on the holidays,” MacGregor said.